Investigating the role of the outer-coordination sphere in [Ni(P(Ph)2N(Ph‑R)2)2]2+ hydrogenase mimics

A series of dipeptide substituted nickel complexes with the general formula, [Ni(P(Ph)(2)N(NNA-amino acid/ester)(2))(2)](BF(4))(2), have been synthesized and characterized (P(2)N(2) = 1,5-diaza-3,7-diphosphacyclooctane, and the dipeptide consists of the non-natural amino acid, 3-(4-aminophenyl)propionic acid (NNA), coupled to amino acid/esters = glutamic acid, alanine, lysine, and aspartic acid). Each of these complexes is an active electrocatalyst for H(2) production. The effects of the outer-coordination sphere on the catalytic activity for the production of H(2) were investigated; specifically, the impact of sterics, the ability of the side chain or backbone to protonate and the pK(a) values of the amino acid side chains were studied by varying the amino acids in the dipeptide. The catalytic rates of the different dipeptide substituted nickel complexes varied by over an order of magnitude. The amino acid derivatives display the fastest rates, while esterification of the terminal carboxylic acids and side chains resulted in a decrease in the catalytic rate by 50-70%, implicating a significant role of protonated sites in the outer-coordination sphere on catalytic activity. For both the amino acid and ester derivatives, the complexes with the largest substituents display the fastest rates, indicating that catalytic activity is not hindered by steric bulk. These studies demonstrate the significant contribution that the outer-coordination sphere can have in tuning the catalytic activity of small molecule hydrogenase mimics.     

Ligand-centred coupling of the alkynyl radical cations [Mo(CCR)(Ph2PCH2CH2PPh2)(η-C7H7)]+ (R = Ph or Bun: crystal structure of the dimeric product [Mo2(Ph2PCH2CH2PPh2)2(η-C7H7)2(μ-C4R2)][PF6]2 (R = Ph)

The radical cations [Mo(CCR)(dppe)(η-C₇H₇)]⁺ (R = Ph or Buⁿ); dppe = Ph₂PCH₂CH₂PPh₂) undergo coupling at C_β of the alkynyl ligand to afford the divinylidene-bridged, dimeric products [Mo₂(dppe)₂(η-C₇H₇)₂(μ-C₄R₂)]²⁺, characterised crystallographically for R = Ph.     

Synthesis and structure of gold complexes [Ph3PR]+[Au(CN)2I2-trans]−, R = Et,CH2Ph,Ph

Russian Chemical Bulletin - Gold complexes [Ph3PR]+[Au(CN)2I2-trans]?, where R = Et (1), CH2Ph (2), Ph (3), were synthesized by the reaction of potassium dicyanodiiodoaurate with...     

Homogeneous and Solid-Gas Hydrogenation of Alkynes in the Presence of the Clusters Fe3(CO)9(ε-RC2 R 1) {R=R 1=Ph, Et; R=Me, R 1=Ph}: Characterization of New Metallacyclic Derivatives

The clusters Fe₃(CO)₉(RC₂ R ¹) (R=R ¹=Ph, Et; R=Me, R ¹=Ph), complexes 1a, 1b, 1c, containing an alkyne bound in perpendicular fashion with respect to a cluster edge, catalyze the hydrogenation of some acetylenes either under homogeneous and solid–gas conditions. We hypothesize that cluster catalysis occurs and that the catalytic activity is related to the coordinating ability of the alkynic substrates. Competition between hydrogenation and formation of metallacyclic byproducts occurs. The new metallacyclic derivatives Fe₃(CO)₆(-CO)₂{(RC₂ R ¹)(R ²C₂ R ³)}, Fe₂(CO)₆{(RC₂ R ¹)(R ²C₂ R ³)} {R=R ¹=Et, R ²=R ³=H, Ph; R ²=Me, R ³=Et, Ph; R ²=H, R ³=Bu ^t . R=R ¹=Ph, R ²=Me, R ³=Et, Ph} (complexes 2, 3) were found both in the homogeneous reaction mixtures and after the solid–gas reactions. The formation of these products lowers the catalytic activity.     

The photo-induced decarbonylation of Cp′M(NO)(CO)2 (M = Cr,Mo, W) with diorgano dichalcogenides (R2E2; E = S,Se; R = Me,Ph)

The photo-induced decarbonylation of CpCr(NO)(CO)₂ (1a) in MeCN solution in the presence of R₂E₂ (E = S, Se; R = Me, Ph) leads to the formation of chalcogenolato-bridged binuclear complexes Cp₂Cr₂(NO)₂(-ER)₂ [E = S; R = Me (2a), Ph (3a); E = Se, R = Me (4a), Ph (5a)] while reactions between CpM(NO)(CO)₂ [M = Mo (1b), W (1c)] and Ph₂E₂ (E = S, Se) result in mononuclear complexes CpM(NO)(EPh)₂ [M = Mo; E = S (9b), Se (10b); M = W, E = S (11c), Se (12c)]. The corresponding reactions of (1b) with Me₂E₂ (E = S, Se) yielded both mono and binuclear complexes: CpMo(NO)(SeMe)₂ (8b), Cp₂Mo₂(NO)₂(-EMe)₂ [E = S (6b), Se (7b)]. The new complexes have been characterized by i.r., ¹H-, ¹³C-n.m.r. spectra and by electron-impact mass spectrometry.     

Reactivity of [trans-R2MoO(NNPhR′)(o-phen)] toward R′PhNNH2 and R′PhNNH3+Cl−, R=Me,Ph and R′=Me,Ph. X-ray structure of [trans-MeClMoO(NNPh2)(o-phen)]

The reactivities of [trans-R₂MoO(NNPhR′)(o-phen)], R=R′=Me (1); R=Me, R′=Ph (2); R=Ph, R′=Me (3); R=R′=Ph (4), toward (i) neutral 1,1-disubstituted hydrazines, R′PhNNH₂ and (ii) 1,1-disubstituted hydrazine hydrochlorides, R′PhNNH₂·HCl, R′=Me, Ph, were studied in acetonitrile. In the first case, no condensation reaction of the free oxo group was observed under different experimental conditions. In the second case, using a 1:1 precursor/hydrazine hydrochloride molar ratio, the oxo group was also unreactive, instead one methyl or phenyl group bonded to molybdenum was displaced as methane or benzene and was subsequently substituted by one chloride ligand affording complexes formulated as [trans-RClMoO(NNPhR′)(o-phen)], R=R′=Me (5); R=Me, R′=Ph (6); R=Ph, R′=Me, (7)·MeCN; R=R′=Ph, (8)·MeCN. Finally, when a 1:2 precursor/hydrazine hydrochloride molar ratio was used, both methyl and phenyl groups were substituted affording complexes formulated as [trans-Cl₂MoO(NNPhR′)(o-phen)], R′=Me (9), R=Ph (10). The new organometallic compounds were characterised by IR, UV–Vis and ¹H NMR spectroscopy while the crystal and molecular structure of 6 was determined by X-ray diffraction analysis.     

Coordination Chemistry and Methylation of Mixed-Substituted Tetraphosphetanes (RP−PtBu)2 (R=Ph,Py)

Synthesis of mixed-substituted tetraphosphetanes (RP−PtBu)₂ (R=Ph ( 4 ), Py ( 5 ); Py=2-pyridyl) is achieved from the condensation of dipyrazolylphosphanes RPpyr₂ (R=Py ( 1 ), Ph ( 3 ); pyr=3,5-dimethylpyrazolyl) as P₁-building block (R−P) and tBuPH₂ in an equimolar ratio. Compound 5 is of special interest since the presence of two pyridyl-substituents as well as the P₄-core allows for a rich coordination chemistry with coinage metal salts [Cu(MeCN)₄][OTf], Ag[OTf] and in situ formed [Au(tht)][OTf] (tht=tetrahydrothiophene). Both tetraphosphetanes undergo alkylation reaction with MeOTf to give a series of tetraphosphetanium and tetraphosphetanediium triflate salts with additional methylation of the pyridyl-moiety in case of 5 resulting in interesting novel cyclic trications. Harsh reaction condition and an excess of MeOTf converts 5 into the cyclic trication [-P(^MePy)PMe₂P(^MePy)PtBu-]³⁺ ( 13 ³⁺; ^MePy=1-methylpyridiniumyl) through the elimination of isobutene. This salt undergoes a complicated rearrangement reaction involving a P−P/P−P bond metathesis to form trication [-P(MePy)₃PtBu-]³⁺ ( 17 ³⁺) when reacted with Me₂PPMe₂.     

The formation of Pt(P–P)(X)(COAr) (X=Cl, I; Ar=Ph, 2-Tioph) complexes via insertion of carbon monoxide

Pt(diphosphine)X(aryl) complexes [diphosphine = 1,3-bis(diphenylphosphino)propane (dppp); aryl=phenyl, 2-thiophenyl; X=Cl, I] have been reacted with carbon monoxide in chloroform. It has been revealed by in situ NMR studies that the starting compounds insert carbon monoxide into the Pt-aryl group resulting in Pt(diphosphine)X{C(O)aryl} complexes. It has been found that the phenyl complexes are much more reactive than the corresponding 2-thiophenyl complexes. Similarly, higher reactivity has been observed with iodo than with the chloro complexes.     

Asymmetric Synthesis of (-)-(2R,3R,6S)-Irnigaine

Introduction　　Asarelativelynewmemberofnaturalalkaloidswith2 ,6 disubstituted 3 piperidinolskeleton ,irnigaine 1wasisolatedfromthetubersofArisarumVulgare (Araceae)in1995byMelhaouiandBode .1Itsstructureandrelativeconfigurationswereelucidatedby1HNMRstudiesandtheabsoluteconfigurationwasproposedonthebasisofitsopti calrotation .1Soonafterthen ,Meyerandhisco workersreportedthefirstsynthesisof (- ) (2R ,3R ,6S) irni gaineandtheconfigurationconfirmation .Althoughtheirsynthesisroutewasshortan…     

Coupling insertion reactions of diphenylbuta-1, 4-diyne into iron-carbene bonds of [Fe2(CO)7{μ-C(Ph)C(NEt2}]. Syntheses and reactivities of the ferracyclopentadiene [Fe2(CO)6{C(Ph)C(NEt2)C(Ph)C(C2Ph)}] with [Fe2(CO)9]

The diiron ynamine complex [Fe₂(CO)₇{-C(Ph)C(NEt₂)}] (1) reacts with the diphenylbuta-1, 4-diyne, PhCC-CCPh, in refluxing hexane to yield three isomer complexes [Fe₂(CO)₆{C(Ph)C(NEt₂)C(Ph)C(C₂Ph}] (2a), [Fe₂(CO)₆{C(Ph)C(NEt₂)C(C₂Ph)C(Ph)}] (2b), and [Fe₂(CO)₆{NEt₂)C(Ph)C(C₂)C(Ph)}] (2c) All three compounds were identified by their¹H NMR spectra. Compounds2a and2c were characterized by single crystal X-ray diffraction analyses. Crystal data: for2a: space group = P2₁/n,a = 17.873(1) Å, = 18.388(6) Å,c = 9.429(3) Å = 91.99(3)°,Z = 4.3751 reflections,R = 0.044; for2c: space group = P2₁/n,a = 40.58(2) å,b = 12.101(9) Å,c = 12.551(5) Å, = 94.29(7)°,Z = 8.4723 reflection,R = 0.076. Complexes2a and2b result from a [2 + 2] cycloaddition between one of the CC triple bonds of the diyne ligand and the FeC carbene bond, whereas2c results from insertion of one of the CC group into the bridging carbene. Addition of [Fe₂(CO)₉] on2a gave two major products, the tripledecker [Fe₃(CO)₈{C(Ph)C(NEt₂)C(C₂Ph)}], (3 and a tetrairon cluster [Fe₄(CO)₁₁{C(Ph)C(NEt₂)C(Ph)C(C₂Ph)}] (4). Both compounds were characterized by single crystal diffraction analyses. Crystal data: for3: space group = P2₁/n,a = 12.039(3) Å,b = 18.046(3) å,c = 15.270(2) Å, = 90.11(2)°,Z = 4, 1430 reflections,R = 0.067; for4 space group = C2/c,a = 18.633(3) Å,b = 21.467(1)_Å,c = 20.742(2) Å, = 115.03(8)°,Z = 8.992 reflections, R = 0.076. Complex4 is based on a spiked triangular cluster with the alkynyl triple bond attached in ₃-parallel mode on the triangular grouping.     

Preparation of ethylene/α-olefins copolymers using (2-RInd)2ZrCl2/MCM-41 (R:Ph,H) catalyst,microstructural study

(2-RInd)₂ZrCl₂ (R:Ph,H) catalyst was supported on MCM-41 and ethylene copolymerization behavior as well as microstructure of copolymers were studied. A steady rate–time profile behavior was observed for homo and copolymerization of ethylene using supported catalysts. It was noticed that increasing the comonomer content can result in lower physical properties. The obtained results indicated that (2-PhInd)₂ZrCl₂/MCM-41 had higher ability of comonomer incorporation than the non-substituted supported catalysts. The CCC, CCE, and ECC (C: comonomer, E: ethylene) triad sequence distribution in backbone of copolymers were negligible, that means no evidence could be detected for comonomer blocks. The polymer characterization revealed that utilizing 1-octene instead of 1-hexene as the comonomer leads to more heterogeneous distribution of chemical composition. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and catalyst. (2-PhInd)₂ZrCl₂/MCM-41 produced copolymers containing narrower distribution of lamellae (0.3–1 nm) than the copolymer produce using Ind₂ZrCl₂/MCM-41 (0.3–1.6 nm).     

Redox properties of the carbyne,aminocarbyne and η2-vinyl complexes trans-[ReCl(LH)(dppe)2][BF4] (LH  CCH2But,CCH2Ph,CNH2 or η2-C(CH2Ph)CH2) and of their parent vinylidene,isocyanide and allene compounds

The redox properties of the carbyne-, aminocarbyne- and η²-vinyl-(metallacyclopropene) complexes trans-[ReCl(LH)(dppe)₂][BF₄] (1; LH  CCH₂R (R Bu^t or Ph), CNH₂ and η²-C(CH₂Ph)CH₂; dppe  Ph₂PCH₂CH₂PPh₂), as well as of their parent vinylidene, isocyanide and allene complexes, trans-[ReClL(dppe)₂] (2; L  CCHR, CNH or

, have been studied by cyclic voltammetry and controlled potential electrolysis in aprotic media. The results are interpreted in terms of anodically- or cathodically-induced β-dehydrogenation processes of complexes (1), to give the corresponding compounds (2) (in the oxidized or the neutral form), as well as of a reversible dissociation of the former into the latter, in a basic solvent. The electrochemical P_L ligand parameter has been estimated for all these ligands.     

Heterobimetallic complexes of palladium(II) bridged by the mixed phosphine–phosphine oxide ligand Ph2PCH2CH2P(O)Ph2

The mixed phosphine–phosphine oxide Ph₂PCH₂CH₂P(O)Ph₂ (dppeO) reacts with either trans-[PdCl₂(PhCN)₂], Na₂[PdCl₄] or trans-[PdCl₂(DMSO)₂] to give trans-[PdCl₂{¹-Ph₂PCH₂CH₂P(O)Ph₂}₂]. Treatment of the latter with the metal chlorides, MCl₂ · nH₂O (M = Mn, Cu, Co, Zn, Hg; n = 4, 2, 6, 1, 0, respectively) or with Me₂SnCl₂ or SnCl₄ · 5H₂O, or with UO₂(NO₃)₂ · 6H₂O or UO₂(OAc)₂ · 2H₂O gives heterobimetallic complexes: trans-[PdCl₂{-Ph₂PCH₂CH₂P(O)Ph₂}₂MX₂] · nH₂O. The cobalt complex (MX₂ = CoCl₂) was unstable in solution (MeOH or EtOH/CHCl₃), and reverts to trans-[PdCl₂{¹-Ph₂PCH₂CH₂P(O)Ph₂}₂] and CoCl₂. trans-[PdCl₂{¹-Ph₂PCH₂CH₂P(O)Ph₂}₂] does not apparently react with either NiCl₂ · 6H₂O or CdCl₂ · 2.5H₂O.     

Enantioselective synthesis of (2S,2′R)-erythro-methylphenidate

A new approach towards the enantioselective synthesis of (2S,2′R)-erythro-methylphenidate (1) is described. The key step in the synthesis utilizes Evans' 4-substituted-2-oxazolidinone chiral auxiliary to control the diastereofacial selectivity in the hydrogenation of enamine intermediate 6, yielding the hydrogenated product 7 with excellent diastereoselectivity. Methanolysis of 7 afforded 1 with excellent enantiopurity.     

Kinetics of Intramolecular Hydrogen Atom Transfer in the Radicals >Si(O·)(R) (R = H,D, CH3, CD3, and C2H5)

Methods are developed for obtaining oxy radicals by the photodecomposition and thermal decomposition of precursors (Si–O)₂Si(N=N–O^·)(R) and (Si–O)₂Si(O–C^·=O)(R). The mechanism of these processes is established. Kinetic data are obtained for the reaction of hydrogen atom transfer in oxy radicals (Si–O)₂Si(O^·)(R) (R = H, D, CH₃, CD₃, and C₂H₅). The activation energies of hydrogen atom transfer are found for three-, four-, and five-membered transition states: 13.5 ± 1, 18 ± 1, and <10 kcal/mol, respectively. For the reaction of H(D) atom transfer in the (Si–O)₂Si(O^·)(H(D)) radical, the kinetic isotope effect is found. Quantum-chemical calculations were used to determine the structures of transition states in the studied processes. Experimental studies were carried out using ESR spectroscopy.     

The preparation and characterisation of a series of cationic bimetallic linear triphos-bridged complexes of the type [Mo (CO) (L,L′ or L″–P) (η2-RC2R′)Cp] [BF4] {L,L′ or L″= [WI2 (CO){PhP(CH2CH2PPh2)2–P,P′} (η2-RC2R′)] (L,R=R′=Me; L′,R=R′=Ph; L″,R=Me,R′=Ph}

Equimolar quantities of [Mo (CO) (η²-RC₂R′)₂Cp] [BF₄] (R=R′=Me Ph R=Me R′=Ph) and L L′ or L″ {L L′ or L″= [WI₂ (CO){PhP(CH₂CH₂PPh₂)₂-PP′} (η²-RC₂R′)]} (L R=R′=Me L′ R=R′=Ph L″ R=Me R′=Ph) react in CH₂Cl₂ at room temperature to give the new bimetallic complexes[Mo (CO) (L L′ or L″–P) (η²-RC₂R′)Cp] [BF₄] (1–9) via displacement of the alkyne ligand on the molybdenum centre The complexes have been characterised by elemental analysis IR and ¹ H NMR spectroscopy and in selected cases by ³¹ P NMR spectroscopy.     

Synthesis and structure of the dimeric organo-antimony (V) imido complex [Ph3Sb(μ-NCH2CH2Ph)]2

The amine PhCH₂CH₂NH₂ undergoes dimetallation by [Ph₃Sb(NMe₂)₂] (1) under mild conditions to give the first structurally authenticated example of an organo-Sb(V) imido complex, [Ph₃Sb(μ-NCH₂CH₂Ph)]₂ (2).     

Chalcogen–acetylide interaction and unusual reactivity of coordinated acetylide with water: synthesis and characterisation of [(η5-C5R5)Fe3(CO)6(μ3-E)(μ3-ECCH2RI)] (R=H,Me; RI=Ph,Fc; E=S,Se) and [(η5-C5R5)MoFe2(CO)6(μ3-S)(μ-SCCH2Ph)] (R=H,Me)

Photolysis of a benzene solution containing [Fe₃(CO)₉(μ₃-E)₂] (E=S, Se), [(η⁵-C₅R₅)Fe(CO)₂(CCR^I)] (R=H, Me; R^I=Ph, Fc), H₂O and Et₃N results in formation of new metal clusters [(η⁵-C₅R₅)Fe₃(CO)₆(μ₃-E)(μ₃-ECCH₂R^I)] (R=H, R^I=Ph, E=S 1 or Se 2; R=Me, R^I=Ph, E=S 3 or Se 4; R=H, R^I=Fc, E=S 5; R=Me, R^I=Fc, E=S 6 or Se 7). Reaction of [Fe₃(CO)₉(μ₃-S)₂]with [(η⁵-C₅R₅)Mo(CO)₃(CCPh)] (R=H, Me), under same conditions, produces mixed-metal clusters [(η⁵-C₅R₅)MoFe₂(CO)₆(μ₃-S)(μ-SCCH₂Ph)] (R=H 8; R=Me 9). Compounds 1–9 have been characterised by IR and ¹H and ¹³C-NMR spectroscopy. Structures of 1, 5 and 9 have been established crystallographically. A common feature in all these products is the formation of new C-chalcogen bond to give rise to a (ECCH₂R^I) ligand.     

Synthesis and structure of Bis(tetraphenylantimony) 1,2-diphenylethanedione dioximate toluene solvate Ph4SbONC(Ph)C(Ph)ONSbPh4 · 2PhCH3 and tetraphenylantimony 2-hydroxy-1,2-diphenylethanone oximate Ph4SbONC(Ph)CH(Ph)OH

Bis(tetraphenylantimony) 1,2-diphenylethanedione dioximate toluene solvate Ph₄SbONC(Ph)C(Ph)NOSbPh₄ · 2 PhCH₃ (I) and tetraphenylantimony 2-hydroxy-1,2-diphenyl(ethanone oximate Ph₄SbONC(Ph)CH(Ph)OH (II) have been synthesized by the reaction of pentaphenylantimony with 1,2-diphenylethane dioxime and 2-hydroxy-1,2-diphenylethanone oxime in toluene. A molecule of compound I is centrosymmetric with an inversion center at the midpoint of the C-C bond in the ethane moiety. A crystal of compound II contains two types of crystallographically independent molecules A and B. Antimony atoms in compounds I and II have a distorted tetragonal bipyramidal surrounding: equatorial CSbC and axial CSbO angles are 114.95(10)°–126.82(11)° and 173.24(9)° (I), 117.2(2)°–122.9(2)° and 178.15(18)° (IIA), and 112.3(2)°–127.7(2)° and 175.09(18)° (IIB), respectively. The Sb-C and Sb-O bond lengths are 2.106(3)–2.182(3) and 2.1344(17) ÅI), 2.118(5)–2.4199(5) and 2.153(4)Å(IIA), and 2.106(5)–2.200(5) and 2.120(4) Å (IIB), respectively. A molecule of compounds I, IIA, and IIB has been found to contain Sb...N intramolecular contacts (2.838(3), 2.867(5), and 2.889(5)Å, respectively). Molecules of compounds IIA and IIB contain O-H...N hydrogen bonds (H...N, 1.91(9) and 2.06(8) Å, respectively).     

Photochemical reactions of [(η 5-C5H5)Mn(CO)3] with Ph2P(S)(CH2) n P(S)Ph2 [n=1, dppm(S)2; 2, dppe(S)2; 3, dppp(S)2]

Six new complexes, Mn(CO)( ⁵-C₅H₅){Ph₂P(S)(CH₂) _n P(S)Ph₂}] (1a–3a) [(1a), n=1; (2a), n=2; (3a), n=3] and [Mn₂(CO)₄( ⁵-C₅H₅)₂(cis--Ph₂P(S)(CH₂) _n P(S)Ph₂)] (1b–3b) [(1b), n=1; (2b), n=2; (3b), n=3] have been synthesized by the photochemical reaction of [( ⁵-C₅H₅)Mn(CO)₃] with Ph₂P(S)(CH₂) _n P(S)Ph₂ [n=1, dppm(S)₂; 2, dppe(S)₂; 3, dppp(S)₂]. The complexes have been characterized by elemental analysis, mass spectroscopy, f.t.-i.r. and ³¹P–[¹H]-n.m.r. spectroscopy. The spectroscopic studies reveal that coordination of the ligand iscis-chelate bidentate in [Mn(CO)( ⁵-C₅H₅){Ph₂P(S)(CH₂) _n P(S)Ph₂}] (1a–3a) and cis-bridging bidentate between two metals in [Mn₂(CO)₄( ⁵-C₅H₅)₂(cis--Ph₂P(S)(CH₂) _n P(S)Ph₂)] (1b–3b).